A new bacteriophage of Clostridium perfringens was isolated which could cause complete lysis of its indicator strain in fluid culture. The adsorption characteristics and one-step growth experiments revealed that the phage rapidly adsorbed to the indicator strain and had a latent period of 45 min. Electron microscopy was performed on both thin sections and partially lysed preparations of infected bacteria at intervals throughout the growth cycle of the phage. This phage, named CPT4, has a head diameter of 64 nm and a striated tail 170 × 10 nm. In addition to these complete phages a number of "petit" phage forms was apparent in lysates. These forms were 55 nm in diameter, possessed no tail, and probably contained no nucleic acid.Morphogenic studies revealed that head forms appeared 30 min postinfection and that tails were present by 35 min. Assembly of mature phage particles seemed complete 40 min postinfection.